The present invention relates to a solid electrolyte having ionic conductivity which can be used for cells, electrochromic display elements (ECD) and sensors.
Various methods have been proposed to produce solid electrolytes. For example, there has been known a method in which an acryloyl-modified polymer having alkylene oxide polymer chain is mixed with an electrolyte salt or a solvent soluble in them and crosslinked by heat, light or an electronic beam to prepare a solid electrolyte having ionic conductivity.
Further, as the known solid electrolytes, there are exemplified a high molecular solid electrolyte prepared by a combination of a trifunctional high polymer having terminal acryloyl-modified alkylene oxide polymer chain, a low molecular alkylene oxide copolymer, polyvinyl chloride and an electrolyte salt (Japanese laid-Open Patent Publication No. 177,409 of 1991) and a solid electrolyte prepared by combining a terminal acryloyl-modified alkylene oxide polymer, an inorganic ionic salt and an organic solvent such as propylene carbonate (Japanese Laid-Open Patent Publication No. 94,501of 1988 corresponding to U.S. Pat. No. 4,908,283).
When these solid electrolytes are used in a cell and other electrochemical elements in place of the electrolytic liquids conventionally used, problems such as leakage of the liquid does not occur and high reliability can be assured advantageously.
However, its conductivity is lower than those of the conventional electrolytic liquids and hence the internal resistance becomes higher and, for example when used as an electrolyte in a cell, only a cell of very low capacity can be prepared disadvantageously.
Furthermore, the materials used are required to have high mechanical strength to match the light weight and thin shape of recent electric devices and the above proposals cannot satisfy it practically.
The object of the present invention is to overcome the above problems and to provide a solid electrolyte having a high conductivity and also having mechanical strength.
We, inventors, have investigated these problems and have found that a solid electrolyte having a high mechanical strength and having a conductivity comparable with the conventional electrolytic liquids and giving no bleed-out of the solvent can be prepared by a procedure in which a trifunctional terminal acryloyl-modified polymer having an alkylene oxide polymer chain consisting of not smaller than a specified number of monomer unit is used and further a solvent is added to it in a range of specified ratio and an electrolyte salt is added and the compound is crosslinked by an irradiation of an active radiation such as light and electron beam and/or heating to complete the present invention.